The dewatering of sludge having a high water content and a high fluidity, such as sewage sludge, requires water to be removed from the sludge beforehand to obtain concentrated sludge having a low fluidity. In particular, in the case of compressing and dewatering of the sludge by a screw press, concentrated sludge obtained by a concentrator is accumulated in a storage tank once; and the sludge taken out of the storage tank is flocculated by adding a flocculant thereto and thereafter is dewatered by the screw press.
Japanese Patent No. 3797551 discloses a rotary concentrator configured to concentrate sludge for the purpose of increasing the dewatering efficiency of a screw press.
Japanese Patent No. 3680994 discloses a method of processing sewage sludge, which includes the steps of accumulating sludge concentrated by a rotary concentrator in a storage tank once and then injecting the concentrated sludge taken out of the storage tank into a screw press.